Asphalt mixes are widely used in road construction and maintenance and majority of asphalt mixes that are used currently are produced by the hot method which is generally known as hot-mix or HMA. This is also known as asphalt concrete which consists of asphalt binder and mineral aggregates. The aggregates could be natural aggregates or processed. Normally processed aggregates are used which have been quarried, crushed, separated into distinct size fractions, washed or otherwise processed to achieve certain performance characteristics of the finished HMA. The aggregates are usually a mixture of various sizes to give desired properties to the asphalt mix as specified in the mix design.
The strength and durability of the asphalt pavements depends on various factors such as the properties of the materials used, the interaction of various materials, the mix-design and construction practices. It is important to attain proper coating of the aggregate with asphalt with optimum binder (asphalt) film thickness and good adhesion of asphalt onto the aggregate, and good cohesive strength of the asphalt to produce a mix that will have good performance during the lifetime of the pavement. The pavements are designed to avoid the various distress types such as permanent deformation, fatigue cracking, low temperature cracking and moisture damage.
Moisture damage is also of great concern. Moisture damage in asphalt mixes can occur by two major pathways. First water will displace asphalt from the aggregate surface especially the ones containing higher amounts of silica since water has a higher affinity for the aggregate surface compared to asphalt and there is lack of chemical bonding of asphalt to the surface. This is known as stripping. Adhesion is the formation of chemical bond between asphalt and the aggregate. Secondly water over a period of time under repeated load can get inside asphalt and reduce the cohesive strength of asphalt. The results of stripping and loss of cohesive strength of the asphalt on the properties of the mix can be conveniently evaluated by the Hamburg wheel tracking test which measures deformation of the mix by a repeated load under water.
It is well known that adhesion promoters which are surface active molecules known as liquid anti-stripping additives or hydrated lime are being used in hot-mix to provide protection against water damage. This solved the problems of water damage with many conventional mixes, but some mixes are unresponsive to conventional anti-stripping additive treatments. It is also well known that the rheology of asphalt can be modified with additives of various types, but these rheology modifying treatments when used alone are not able to solve all problems of water damage.
The invention is concerned with the technical problem of providing an improved bitumen or asphalt, in particular for the production of road surfaces. More specifically, the present inventors have found that a novel combination of surfactants and asphalt rheology modifiers can influence the adhesion and cohesion properties of asphalt to significantly improve the resistance of hot-mixes to moisture damage. This results in superior asphalt or a mixture of bitumen (asphalt) with aggregates which is more resistant to water damage. This is the first instance that a unique combination of surfactants and rheology modifiers have been used as a single package, which demonstrate much improved performance compared to conventional anti-stripping additive treatment.